Mario Orefice

Synthetic function analysis of large printed structures: the solution space sampling approach

This work proposes an algorithm based on the numerical definition of entire domain basis functions to be used in the full-wave method of moments (MoM) solution for large printed antennas. After a block partitioning of the structure, entire domain basis functions are generated and then employed in the global solution process. The generation algorithm and a possible selection model is presented in detail. The method permits a strong reduction of memory occupation and computation time. A numerical example for a 4 /spl times/ 2 array of stacked patches is presented.

Controlling the Bandlimits of TE-Surface Wave Propagation Along a Modulated Microstrip-Line-Based High Impedance Surface

A hybrid numerical-analytical method for the characterization of the propagation of the transverse-electric surface waves along a high impedance surface (HIS) is presented. The HIS is obtained by a 2-D periodic repetition of a rectangular unit cell on a Cartesian grid. The unit cell consists of a microstrip line with variable width immersed in a grounded multilayer dielectric substrate. Inside the unit cell, the effective value of the dielectric is sinusoidally modulated along the direction of the microstrip line, and the dimension of the unit cell is equal to the period of the modulation. On the basis of the modulation parameters, limits of the stop/pass bands are determined analytically employing Mathieus functions. The synthesis of the shape of the microstrip line that guarantees the desired modulation requires the numerical determination of the phase velocity - line width relationship which is not known in closed form for the considered unbounded open structure. The limits of the pass/stop bands determined analytically are in very good agreement with those found numerically and measured values for different modulation parameters.

Controlled Leaky-Wave Radiation From a Planar Configuration of Width-Modulated Microstrip Lines

Planar leaky-wave antenna (LWA) designs that utilize a printed surface wave (SW) source are presented. Specifically, by the addition of a periodic arrangement of width-modulated microstrip lines on top of a grounded dielectric slab (GDS), a sinusoidally modulated reactance surface (SMRS) can be realized, providing appropriate conditions for leaky wave (LW) radiation. In addition, a transition section near the SW source improves antenna matching, while also, controlling the leakage rate and aperture distribution. A numerically computed dispersion diagram (DD) for the periodic structure is also calculated in terms of Mathieu functions. Full-wave simulations and measurements are in agreement with the developed numerical model and results suggest that these LWAs can offer broadside radiation as well as continuous beam scanning with radiation efficiencies of more than 85%. In addition, the investigated width-modulated microstrip lines offer ease of fabrication and may also be useful in the design of new periodic structures for wave guidance and other low-cost printed circuits and antennas.

Application of numerical regularization options to the integral-equation analysis of printed antennas

In this letter, a novel numerical technique is applied to the analysis of printed antennas. The technique transforms the first-kind electric-field integral equation (EFIE) into a regularized second-kind equation, via extraction of two singular frequency-independent operators and their numerical inversion. Two options are presented in which the inversion is based on the eigenfunctions of these singular operators, that appear to be a generalization of the TM and TE modes of a magnetic-wall cavity, coupled by the edge singularities. The example of application shows favorable convergence properties.

Efficient spectral evaluation of mutual coupling between planar antennas

This work deals with the evaluation of mutual coupling in arrays of apertures or printed radiators and other similar problems. Two analytical-based numerical integration techniques will be described, for the efficient evaluation of the spectral reaction integrals between two arbitrary functions on separated domains in a general stratified medium. These techniques employ novel schemes of contour deformation. The spectral domain formulation is used, and integration is carried out in Cartesian coordinates, taking the χ axis along the direction adjoining the centers of the two basis functions involved. In both techniques the kχ contour is deformed along the negative imaginary axis in order to turn the oscillating shift exponential into a decaying term. A robust scheme is obtained, with yet additional advantages in the case where many coupling terms at different distances are to be evaluated (as in alignments within arrays). Validation against published data and an application example are presented, along with a discussion of the numerical performances.

Propagation of Electromagnetic Waves in a Sinusoidally Modulated Dielectric Substrate

A single-layer microstrip structure with variable line width is considered in order to create, by periodic repetition, an electromagnetic bandgap structure. The width of the line is varied in such a way as to guarantee a sinusoidally modulated value of the effective dielectric constant along the longitudinal direction. By repeating periodically the structure in the orthogonal direction, a high-impedance surface is obtained. Continuous and discrete line configurations are considered, and the performances of the two-dimensional structure with respect to the uniform line case are compared

A modified Butler matrix for tapered excitation of scanned arrays

We present a modified Butler matrix that allows the excitation distribution of an array to be tapered. The output section of the matrix is replaced by a network of branch-line hybrids, some of them unbalanced, to modify the power distribution in the output lines. This technique allows flexibility in the choice of the excitation coefficient and eliminates some of the drawbacks of conventional solutions.

Spectral-domain analysis of printed antennas of general shape on cylindrical substrates

We deal with the full-wave analysis of microstrip antennas on cylindrical substrates, in edge-fed (monolithic) and EMC configurations. We employ the electric field integral equation-method of moment (EFIE-MoM) approach in the spectral domain, and subsectional basis functions that allow the description of patches and feed systems of general form. The spectral asymptotic behavior is extracted, increasing the overall efficiency.

Dyadic Green's function in bounded media

A new theory for the evaluation of the dyadic Greens functions in a homogeneous medium bounded by perfectly conducting walls is presented. The peculiarities of this theory are 1) the Greens functions are systematically and explicitly decomposed in a singular and an analytical part, and 2) these two parts are formulated in a general manner, i.e., independent on the boundaries. As an application, the Greens functions in a conical guide are evaluated.

Some preliminary results on conformal Reflectarrays

In this paper, the characteristics of Reflectarray Antennas printed on convex curved surfaces are analyzed. In particular, results on the radiation performances of different Reflectarrays designed to be mounted on cylinders with different radii of curvature are presented and discussed.